Buggy code:
public class JPAExtension implements Extension { public static final String SUBSYSTEM_NAME = "jpa" ; private static final JPAExtension . JPASubsystemElementParser parser = new JPAExtension . JPASubsystemElementParser ( ) ; private static final DescriptionProvider DESCRIPTION = new DescriptionProvider ( ) { @ Override public ModelNode getModelDescription ( Locale locale ) { } } ; private static ModelNode createAddOperation ( String defaultDatasource ) { } @ Override public void initialize ( ExtensionContext context ) { <START_BUG> SubsystemRegistration registration = context . registerSubsystem ( JPAExtension . SUBSYSTEM_NAME , 1 , 0 ) ; <END_BUG> final ManagementResourceRegistration nodeRegistration = registration . registerSubsystemModel ( JPAExtension . DESCRIPTION ) ; PersistenceUnitRegistryImpl persistenceUnitRegistry = new PersistenceUnitRegistryImpl ( ) ; JPASubSystemAdd subsystemAdd = new JPASubSystemAdd ( persistenceUnitRegistry ) ; nodeRegistration . registerOperationHandler ( OPERATION_NAME , subsystemAdd , subsystemAdd , false ) ; nodeRegistration . registerOperationHandler ( JPASubSystemRemove . OPERATION_NAME , INSTANCE , INSTANCE , false ) ; nodeRegistration . registerOperationHandler ( DESCRIBE , JPAExtension . JPADescribeHandler . INSTANCE , JPAExtension . JPADescribeHandler . INSTANCE , false , PRIVATE ) ; nodeRegistration . registerReadWriteAttribute ( DEFAULT_DATASOURCE , null , JPADefaultDatasourceWriteHandler . INSTANCE , CONFIGURATION ) ; registration . registerXMLElementWriter ( JPAExtension . parser ) ; try { PersistenceProviderLoader . loadDefaultProvider ( ) ; } catch ( ModuleLoadException e ) { JpaLogger . JPA_LOGGER . errorPreloadingDefaultProvider ( e ) ; } try { PersistenceProviderAdaptor provider = PersistenceProviderAdaptorLoader . loadPersistenceAdapterModule ( ADAPTER_MODULE_DEFAULT ) ; final ManagementAdaptor managementAdaptor = provider . getManagementAdaptor ( ) ; if ( ( managementAdaptor != null ) && ( context . isRuntimeOnlyRegistrationValid ( ) ) ) { DescriptionProvider JPA_SUBSYSTEM = new DescriptionProvider ( ) { @ Override public ModelNode getModelDescription ( Locale locale ) { ModelNode subsystem = new ModelNode ( ) ; subsystem . get ( org . jboss . as . controller . descriptions . ModelDescriptionConstants . DESCRIPTION ) . set ( "Runtime<seq2seq4repair_space>information<seq2seq4repair_space>about<seq2seq4repair_space>JPA<seq2seq4repair_space>use<seq2seq4repair_space>in<seq2seq4repair_space>the<seq2seq4repair_space>deployment." ) ; subsystem . get ( ATTRIBUTES ) . setEmptyObject ( ) ; subsystem . get ( "operations" ) ; subsystem . get ( CHILDREN , managementAdaptor . getIdentificationLabel ( ) , org . jboss . as . controller . descriptions . ModelDescriptionConstants . DESCRIPTION ) . set ( ( ( "Runtime<seq2seq4repair_space>information<seq2seq4repair_space>about<seq2seq4repair_space>" + ( managementAdaptor . getIdentificationLabel ( ) ) ) + "<seq2seq4repair_space>use<seq2seq4repair_space>in<seq2seq4repair_space>the<seq2seq4repair_space>deployment." ) ) ; subsystem . get ( CHILDREN , managementAdaptor . getIdentificationLabel ( ) , MIN_OCCURS ) . set ( 0 ) ; return subsystem ; } } ; final ManagementResourceRegistration jpaSubsystemDeployments = registration . registerDeploymentModel ( JPA_SUBSYSTEM ) ; managementAdaptor . register ( jpaSubsystemDeployments , persistenceUnitRegistry ) ; } } catch ( ModuleLoadException e ) { JpaLogger . JPA_LOGGER . errorPreloadingDefaultProviderAdaptor ( e ) ; } } @ Override public void initializeParsers ( ExtensionParsingContext context ) { } private static class JPADescribeHandler implements OperationStepHandler , DescriptionProvider { static final JPAExtension . JPADescribeHandler INSTANCE = new JPAExtension . JPADescribeHandler ( ) ; public void execute ( OperationContext context , ModelNode operation ) throws OperationFailedException { } @ Override public ModelNode getModelDescription ( Locale locale ) { } } static class JPASubsystemElementParser implements XMLStreamConstants , XMLElementReader < List < ModelNode > > , XMLElementWriter < SubsystemMarshallingContext > { @ Override public void readElement ( XMLExtendedStreamReader reader , List < ModelNode > list ) throws XMLStreamException { } private ModelNode parseJPA ( XMLExtendedStreamReader reader ) throws XMLStreamException { } @ Override public void writeContent ( final XMLExtendedStreamWriter writer , final SubsystemMarshallingContext context ) throws XMLStreamException { } } }

Fix:
SubsystemRegistration registration = context . registerSubsystem ( JPAExtension . SUBSYSTEM_NAME , 1 , 1 ) ;